Ultrastructural studies showed that the early changes induced in rat left ventricular myocardium by administration of allylamine, a highly cardiotoxic aliphatic amine used in industry, consist of : 1) interstitial edema; 2) activation of interstitial and endothelial cells, and 3) acute myocardial necrosis, with hypercontraction bands, myofibrillar damage, dissolution of Z bands and dense intramitochondrial inclusions.